Unlike some of the other functionality provided by Logkit,
the logging functionality does not wrap an underlying log provider.
Why not? Because, in a past life, I worked as a Java developer and
therefore understand that log wrappers will bring you nothing but pain
and unhappiness.
Instead of being a log wrapper, this functionality encourages
applications to use logrus. Logrus is already widely used in GitLab.
What benefit does this functionality add:
* Consistent configuration of logrus
* Importantly, this functionality allows labkit itself to write logs.
* This will allow us to add better logging, as well as standardised
access loggers, exception loggers etc
Co-authored-by: Zeger-Jan van de Weg <zegerjan@gitlab.com>

This change adds support for passing trace and span propagation details
from parent to child process via environment variables.
The change also ensures that the GITLAB_TRACING variable is correctly
passed to child processes.